Solder material and bonded structure

ABSTRACT

Solder material used in soldering of an Au electrode including Ni plating containing P includes Ag satisfying 0.3≦[Ag]≦4.0, Bi satisfying 0≦[Bi]≦1.0, and Cu satisfying 0&lt;[Cu]≦1.2, where contents (mass %) of Ag, Bi, Cu and In in the solder material are denoted by [Ag], [Bi], [Cu], and [In], respectively. The solder material includes In in a range of 6.0≦[In]≦6.8 when [Cu] falls within a range of 0&lt;[Cu]&lt;0.5, In in a range of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu] falls within a range of 0.5≦[Cu]≦1.0, In in a range of 5.2≦[In]≦6.8 when [Cu] falls within a range of 1.0&lt;[Cu]≦1.2. A balance includes only not less than 87 mass % of Sn.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure mainly relates to solder material of solder pasteor the like used in soldering in an electronic circuit board, and abonded structure using the solder material.

2. Background Art

For soldering an electronic circuit board and an electronic component toeach other, solder material having a composition of Sn—Ag—Bi—Inconsisting of four types of elements is used, which is disclosed in, forexample, Patent Literatures 1 and 2. In such solder material, thermalfatigue properties with respect to fatigue fracture occurring due tothermal stress accompanied by a temperature change are enhanced by atechnique using an effect of solid solution. The solid solution denotesa technique of preventing deterioration of solder material by replacinga part of metal atoms arranged in a lattice with a different metal atomso as to distort such a lattice.

CITATION LIST Patent Literature

PTL 1: Japanese patent No. 3040929

PTL 2: Japanese Patent Application Unexamined Publication No.2010-179336

SUMMARY OF THE INVENTION

Solder material in accordance with the present disclosure is soldermaterial used in soldering of an Au (gold) electrode including Ni(nickel) plating containing P (phosphorous), including:

-   -   Ag (silver) satisfying 0.3≦[Ag]≦4.0;    -   Bi (bismuth) satisfying 0≦[Bi]≦1.0; and    -   Cu (copper) satisfying 0<[Cu]≦1.2; and further including:    -   In (indium) in a range of 6.0≦[In]≦6.8 when [Cu] falls within a        range of 0<[Cu]<0.5;    -   In in a range of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu]        falls within a range of 0.5≦[Cu]≦1.0;    -   In in a range of 5.2≦[In]≦6.8 when [Cu] falls within a range of        1.0<[Cu]≦1.2,

with a balance including only not less than 87 mass % of Sn (tin),

where contents (mass %) of Ag, Bi, Cu and In in the solder material aredenoted by [Ag], [Bi], [Cu], and [In], respectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph for illustrating solder material in accordance with anembodiment, showing results of a reliability test of an alloy having acomposition of Sn-3.5 mass % Ag-0.5 mass % Bi to which In is added.

FIG. 2A is a sectional view schematically showing an Au electrode.

FIG. 2B is a sectional view schematically showing a Cu electrode.

FIG. 3A is a sectional view showing a state of solder material suppliedonto an electrode (before soldering) for measuring an In content (indiumcontent) after an electrode and solder material are bonded to eachother.

FIG. 3B is a sectional view showing a state of solder portion formed onthe electrode (after soldering) for measuring the In content after theelectrode and the solder material are bonded to each other.

FIG. 4 is a graph for illustrating the solder material in accordancewith this embodiment, showing analysis results of the In content insidethe solder of each of the Cu electrode and two types of Au electrodesusing solder material having a composition of Sn-3.5 mass % Ag-0.5 mass% Bi-6.0 mass % In after soldering.

FIG. 5 is a graph for illustrating solder material in accordance withthe embodiment, showing analysis results of the In content inside thesolder of two types of Au electrodes having different film thicknessesusing solder material having a composition of Sn-3.5 mass % Ag-0.5 mass% Bi-6.0 mass % In to which Cu is added, after soldering.

FIG. 6 is a graph for illustrating solder material in accordance withthe embodiment, showing a solid phase line and a liquid phase line ofsolder material having a composition of Sn-3.5 mass % Ag-0.5 mass %Bi-6.0 mass % In to which Cu is added.

FIG. 7 is a graph showing a relation between a Cu content and the Incontent in the solder material before the upper limit of the Cu contentis not considered in accordance with the embodiment.

FIG. 8A is a sectional view schematically showing a structure before aCu substrate electrode of an electronic circuit board and a Cu componentelectrode of an electronic component are soldered to each other.

FIG. 8B is a sectional view showing a structure after the Cu substrateelectrode of the electronic circuit board and the Cu component electrodeof the electronic component are soldered to each other.

FIG. 9 is a graph showing relation between the Cu content and the Incontent in the solder material in accordance with the embodiment.

FIG. 10 is a sectional view schematically showing a bonded structure inaccordance with the embodiment.

FIG. 11A is a sectional view schematically showing a structure beforethe Au substrate electrode of the electronic circuit board and the Cucomponent electrode of the electronic component are soldered to eachother.

FIG. 11B is a sectional view schematically showing a structure after theAu substrate electrode of the electronic circuit board and the Cucomponent electrode of the electronic component are soldered to eachother.

FIG. 12A is a sectional view schematically showing a structure beforethe Cu substrate electrode of the electronic circuit board and the Aucomponent electrode of the electronic component are soldered to eachother.

FIG. 12B is a sectional view schematically showing a structure after theCu substrate electrode of the electronic circuit board and the Aucomponent electrode of the electronic component are soldered to eachother.

FIG. 13A is a sectional view schematically showing a structure beforethe Au substrate electrode of the electronic circuit board and the Aucomponent electrode of the electronic component are soldered to eachother.

FIG. 13B is a sectional view schematically showing a structure after theAu substrate electrode of the electronic circuit board and the Aucomponent electrode of the electronic component are soldered to eachother.

FIG. 14 is a schematic sectional view of a bonded structure using aconventional solder material.

DETAILED DESCRIPTION OF THE INVENTION

In an electronic circuit board, as disclosed in PTL 2, in general, a Cu(copper) substrate electrode whose electrode material is Cu is used inmany cases.

However, since vehicle-mounted products such as an ECU (Engine ControlUnit), a DC/DC converter, an inverter, and a head lamp require highbonding reliability, an Au substrate electrode, to which Au (gold) flashplating is applied by flash treatment of carrying out thin plating for ashort time, may be used.

As an example, FIG. 14 shows a sectional view of bonded structure 900.Bonded structure 900 is configured by bonding electronic circuit board930 having Au substrate electrodes 931 and 932 to electronic component920 having Cu component electrodes 921 and electronic component 940having Au component electrodes 941 by soldering. Au substrate electrodes931 of electronic circuit board 930 and Cu component electrodes 921 ofelectronic component 920 are bonded to each other with solder portions911. Furthermore, Au substrate electrodes 932 of electronic circuitboard 930 and Au component electrodes 941 of electronic component 940are bonded to each other with solder portion 912. Solder portions 911and 912 are formed of solder material having a composition of Sn(tin)-Ag (silver)-Bi (bismuth)-In (indium).

In the solder material having a composition of Sn—Ag—Bi—In, In issolid-dissolved in a lattice of Sn, so that the thermal fatigueproperties are enhanced. Specifically, solder material having acomposition of, for example, Sn-3.5 mass % Ag-0.5 mass % Bi-6 mass % In,is used. Ag is added to improve alloy strength by depositionstrengthening and to lower the melting point. Bi is added to lower themelting point.

However, it has been found that the solder material having a compositionof Sn—Ag—Bi—In does not necessarily have high thermal fatigue propertiesin soldering to the Au substrate electrode.

The present inventors have analyzed the reason thereof as follows. Thatis to say, in the solder material having a composition of Sn—Ag—Bi—In,the thermal fatigue properties are changed by an In content (indiumcontent). The thermal fatigue properties herein are defined as a numberof cycles in which occurrence of cracks is not found in across-sectional observation of the solder portion after a heat cycletest is carried out under the test conditions of −40° C./150° C.(conditions for the reliability test of a vehicle-mounted product). Forexample, when a case where the composition of the solder material aftersoldering is Sn-3.5 mass % Ag-0.5 mass % Bi-6 mass % In and a case wherethe composition is Sn-3.5 mass % Ag-0.5 mass % Bi-5.5 mass % In arecompared with each other, the numbers of cycles in the heat cycle testsare 2300 cycles and 2150 cycles, respectively. That is to say, as thereduction of In, the number of cycles (thermal fatigue properties) isalso reduced.

The alloy strength on the thermal fatigue properties is increased untilthe In content is increased to about 6 mass %, and is reduced when theIn content exceeds this value. In other words, when the In content isabout 6 mass %, the number of cycles in the heat cycle test isincreased, so that the thermal fatigue properties are highest.Therefore, in order to efficiently use the solid solution effect by In,it is desirable to precisely control the In content in the soldermaterial.

The Au substrate electrode has a structure in which Ni (nickel) platinghaving a film thickness of 1 to 5 μm is applied to the Cu electrode,and, furthermore, Au flash plating having a film thickness of 0.03 to0.07 μm is applied to the Ni plating. In soldering with heating, Au isdissolved in Sn—Ag—Bi—In, and Ni plating is exposed. The Ni plating hasa composition of 90 mass % Ni and 10 mass % P (phosphorous). Since thereactivity between In and P is high, In and P are reacted with eachother to generate a compound InP having a composition of In—P. Then, Insolid-dissolved in a lattice of Sn, which contributes to improvement ofthe thermal fatigue properties, is reduced, and the substantial Incontent is reduced.

Herein, in order to enhance the thermal fatigue properties of the Ausubstrate electrode whose In content after soldering is reduced,increasing of the In content in the solder material having a Sn—Ag—Bi—Incomposition before soldering is considered. However, electroniccomponents to be mounted on one electronic circuit board may include acomponent having an Au component electrode and a component having a Cucomponent electrode. These two type of component electrodes havedifferent changes of the In content in the solder material, and thereduction amount of the In content is small in the Cu componentelectrode. Therefore, in order to prevent the In reduction aftersoldering of the Au substrate electrode, even if the In content in thesolder material before soldering is increased, the thermal fatigueproperties of the Cu component electrode are reduced. Thus, it has beennecessary to consider means other than the addition of In.

The solder material of the present disclosure has been invented in viewof the above-mentioned problems, and is effective to form a solderportion having excellent thermal fatigue properties even if an Auelectrode and a Cu electrode are mixed, for example, when an electroniccircuit board and an electronic component are bonded to each other bysoldering.

Hereinafter, an embodiment is described in detail with reference todrawings.

Embodiment

Firstly, a principle on solder material in accordance with thisembodiment is described in detail.

FIG. 1 is a graph for illustrating solder material in accordance withthis embodiment, showing results of a reliability test of an alloyhaving a composition of Sn-3.5 mass % Ag-0.5 mass % Bi to which In isadded.

An In content (indium content) in the abscissa of the graph shown inFIG. 1 is a substantial In content of In solid-dissolved in a solderportion, more specifically, in a lattice of Sn, after soldering.

A number of test cycles in the ordinate of the graph shown in FIG. 1shows the number of cycles in which occurrence of cracks has not beenfound in a cross-sectional observation of the solder portion after aheat cycle test is carried out. The test is carried out at −40° C./150°C. on an FR5 substrate on which a chip capacitor having a 1608 size (1.6mm×0.8 mm) is mounted and whose FR grade (Flame Retardant grade) is FR-5grade.

In the reliability test of vehicle-mounted products mounted in thevicinity of an engine of an automobile, requirements specificationrequires that the number of cycles is not less than 2000 cycles as anin-vehicle requirement. Herein, when the number of cycles is not lessthan 2000 cycles, the thermal fatigue properties are defined to besufficiently satisfied.

According to the graph shown in FIG. 1, when the content of Insolid-dissolved in the solder portion after soldering is 5.5 mass %(2150 cycles), 6.0 mass % (2300 cycles) and 6.5 mass % (2200 cycles),the number of cycles is not less than 2000 cycles. When the In contentis not more than 5.0 mass % or not less than 7.0 mass %, the number ofcycles is less than 2000 cycles.

An approximating curve drawn by using the above-mentioned numeric datais shown in FIG. 1 as a graph of the quadratic function represented bythe following mathematical formula.

(Number of Test Cycles)=−410.7×(In content)²+4919.6×(In content)−12446

Herein, a range of the In content enabling not less than 2000 cycles ofthe number of cycles as the in-vehicle requirement to be assured isabout 5.2 to 6.8 mass % with a control width being about ±0.8 mass %.

Furthermore, since a fluctuation range of the In content in a solderalloy in mass production is about ±0.5 mass %, the median value of theIn content is desirably not less than 5.7 (=5.2+0.5) mass % and not morethan 6.3 (=6.8-0.5) mass %.

Next, mainly with reference to FIGS. 2A to 4, an influence of Pcontained in the Ni plating is described. In order to examine thisinfluence, test samples for measurement shown in FIGS. 2A and 2B areused as Au electrode 40 and Cu electrode 50.

FIG. 2A is a sectional view schematically showing Au electrode 40. FIG.2B is a sectional view schematically showing Cu electrode 50.

FIGS. 3A and 3B are schematic illustration views showing a state ofmeasuring an In content after electrode 3 and solder material 1 arebonded to each other. Electrode 3 is an Au electrode or a Cu electrode,and solder material 1 has a composition of Sn-3.5 mass % Ag-0.5 mass %Bi-6.0 mass % In. FIG. 3A is a sectional view showing a state beforesolder material 1 supplied onto electrode 3 is heated (beforesoldering), and FIG. 3B is a sectional view showing a state of solderportion 2 in which solder material 1 supplied onto electrode 3 isheated, melted and wet-spread (after soldering).

Generally used Au electrode 40 includes Cu electrode 10, Ni plating 20provided on Cu electrode 10, and Au flash plating 30 provided on Niplating 20 as shown in FIG. 2A. Cu electrode 10 is formed of a Cu foilhaving a film thickness of, for example, 35 μm. Ni plating 20 has a filmthickness of, for example, 1 to 5 μm, and is provided as electrolessplating which does not require an electric current to flow unlikeelectroplating. Au flash plating 30 has a film thickness of, forexample, 0.03 to 0.07 μm. On the other hand, Cu electrode 50 is formedof a Cu foil having a film thickness of 35 μm as shown in FIG. 2B.

Au electrode 40 and Cu electrode 50 as mentioned above are used as asubstrate electrode of an electronic circuit board, or as a componentelectrode of an electronic component. The technique of the presentdisclosure includes a case in which an electronic circuit board isprovided with an Au substrate electrode and a Cu substrate electrode anda case in which an electronic component is provided with an Au componentelectrode and a Cu component electrode.

In this embodiment, two types of Au electrodes are prepared as testsamples for the reliability test. A first Au electrode includes Niplating having a film thickness of 5 μm and Au flash plating having afilm thickness of 0.07 μm. This assumes that one of a substrate side ora component side is the Au electrode. A second Au electrode includes Niplating having a film thickness of 10 μm, and Au flash plating having afilm thickness of 0.07 μm. This assumes that both the substrate side andthe component side are Au electrodes, and that an influence of P ismaximum. When the solder material is melted into a liquid duringsoldering, Au and Ni instantaneously diffuse to react with the soldermaterial. Therefore, by doubling the thickness of Ni containing P, thecase in which both the substrate side and the component side are Auelectrodes can be simulated.

As shown in FIG. 3A, solder material having a composition of Sn-3.5 mass% Ag-0.5 mass % Bi-6.0 mass % In, which has a circular shape having adiameter φ of 5 mm and a shape having a thickness t of 0.15 mm seen inthe plan view, is supplied onto electrode 3. Electrode 3 is any one ofthe above-mentioned two types of electrodes, that is, the Au electrodeand the Cu electrode. Thereafter, electrode 3 supplied with soldermaterial 1 is heated on a hot plate at 240° C. for 30 seconds, and thengradually cooled at room temperature. Thus, solder material 1 is formedinto solder portion 2 having a shape as shown in FIG. 3B.

As mentioned above, the test samples of solder portion 2 are obtained.Next, solder portion 2 is polished so that the longitudinal sectionthereof appears, and the In content of the center part of thelongitudinal section is measured by analyzing by a method using EDX(Energy Dispersive X-ray spectroscopy). The center part herein denotes apart corresponding to a position at ½ of the thickness of solder portion2 and at ½ of wet-spread width A of solder portion 2.

FIG. 4 is a graph for illustrating the solder material in accordancewith this embodiment, showing analysis results of the In content insidethe solder of the Cu electrode and two types of Au electrodes usingsolder material having a composition of Sn-3.5 mass % Ag-0.5 mass %Bi-6.0 mass % In after soldering.

The substantial In content of In solid-dissolved in a lattice of Sncontributing to improvement of the thermal fatigue properties is reducedfrom 6.0 mass % as the initial In content. The In content is 5.9 mass %in the Cu electrode, 5.1 mass % in the Au electrode including Ni platingwhose film thickness is 5 μm, and 5.1 mass % in the Au electrodeincluding Ni plating whose film thickness is 10 μm.

In the Au electrode, Au diffuses to the inside of the solder material atthe time of heating, and Ni plating having a composition of 90 mass % Niand 10 mass % P, which is formed under the Au flash plating, is exposed.

Thus, since Sn included in the solder material is reacted with Ni togenerate a Ni₃Sn₄ compound, the Ni content is reduced and the P contentis increased at a solder material side of the Ni plating. A portion inwhich P is concentrated, P per unit area that is brought into contactwith the solder material is increased. Consequently, the productionamount of the compound InP is increased and In solid-dissolved in thelattice of Sn is reduced, so that the substantial In content in the caseof the Au electrode is largely reduced as compared with the case of theCu electrode.

Since the range of the In content corresponding to the in-vehiclerequirement is about 5.2 to 6.8 mass %, the case of the Au electrodementioned above does not satisfy the in-vehicle requirement.

Note here that the specific gravity of the Ni plating is 7.9 g/cm³. Amass of P contained in the Ni plating can be calculated from 7.9×T×S×0.1by using film thickness T of the Ni plating and area S of the Niplating, and the mass of P contained in the Ni plating fluctuates inproportion to film thickness T of the Ni plating.

Based on such a phenomenon, the present inventors have found that it iseffective to reduce the production amount of a Ni₃Sn₄ compound, in orderto suppress the concentration of P that is a cause of the increase inthe production amount of an InP compound.

Examples of elements for generating an intermetallic compound with Sninclude Zn, Co, Mn, and the like. Among these elements, an element whichhas been found to have a high effect is Cu. Cu is reacted with Sn togenerate a Cu₆Sn₅ compound.

Herein, the solder material in accordance with this embodiment isdescribed more specifically with reference to FIGS. 5 and 6.

FIG. 5 is a graph for illustrating solder material in accordance withthe embodiment, showing analysis results of the In content inside thesolder of two types of Au electrodes having different film thicknessesusing solder material having a composition of Sn-3.5 mass % Ag-0.5 mass% Bi-6.0 mass % In to which Cu is added, after soldering. The filmthicknesses of the Ni plating in the two types of Au electrodes are 5 μmand 10 μm, and the film thickness of the Au flash plating is uniformly0.07 μm.

FIG. 6 is a graph for illustrating solder material in accordance withthe embodiment, showing solid phase line 601 and liquid phase line 602of the solder material having a composition of Sn-3.5 mass % Ag-0.5 mass% Bi-6.0 mass % In to which Cu is added.

Firstly, with reference to FIG. 5, the lower limit of the Cu content isdescribed.

Herein, an analysis is carried out by the method mentioned above so asto measure the In content after soldering to the Au electrode.

The test samples of the solder material are produced as follows.

Firstly, 89.5 g of Sn is placed in a ceramic crucible, and the crucibleis stood still in an electric jacket heater whose temperature has beenadjusted to 500° C.

Next, melting of Sn is observed, and then 6.0 g of In is placed into thecrucible, followed by stirring for three minutes.

Next, 0.5 g of Bi is placed into the crucible, followed by stirring forfurther three minutes.

Next, 3.5 g of Ag is placed into the crucible, followed by stirring forfurther three minutes.

Next, a predetermined amount of Cu is placed into the crucible, followedby stirring for further three minutes.

Note here that each element of Sn, Bi, Ag, and Cu used herein includes aslight amount of impurities.

Thereafter, the crucible is taken out from the electric jacket heater,and cooled by immersing it into a container filled with 25° C. water.

In FIG. 5, the In content in the Au electrode including the Ni platinghaving a film thickness of 5 μm is plotted with “A.” The In contentafter soldering to the Au electrode including the Ni plating having afilm thickness of 5 μm is denoted as follows. (1) It is 5.1 mass % whenthe Cu content is zero, but (2) it is increased because the reduction ofIn is suppressed when the Cu content is increased, (3) it is 5.2 mass %when the Cu content is 0.4 mass %, and then (4) it is 5.99 mass % whenthe Cu content becomes 0.9 mass %. In this way, when the Cu content ischanged from zero to 0.9 mass %, the In content is changed from 5.1 mass% to 5.99 mass %.

In FIG. 5, the In content in the Au electrode including the Ni platinghaving a film thickness of 10 μm is plotted with “o.” The In contentafter soldering to the Au electrode including the Ni plating having afilm thickness of 10 μm is denoted as follows, (1) It is 5.1 mass % whenthe Cu content is zero, but (2) it is increased because the reduction ofIn is suppressed when the Cu content is increased, (3) it is 5.21 mass %when the Cu content is 0.5 mass %, and then (4) it is 5.83 mass % whenthe Cu content is 0.9 mass %. In this way, when the Cu content ischanged from zero to 0.9 mass %, the In content is changed from 5.1 mass% to 5.83 mass %.

When a case where the film thickness of the Ni plating is 5 μm and acase where it is 10 μm are compared with each other, the change amountof the In content is larger in the Ni plating having a film thickness of10 μm in which both the substrate electrode and the component electrodeare assumed to be an Au electrode. Therefore, it is desirable that thelower limit value of the Cu content is calculated from numeric values inthe case where the film thickness of the Ni plating is 10 μm.

In the case where the film thickness of the Ni plating is 10 μm, when anapproximate straight line is drawn using numeric values at the time whenthe Cu content is from 0.5 mass % to 0.9 mass %, a graph of a linearfunction represented by the following mathematical formula is obtained.

(In content)=1.55×(Cu content)+4.428

Therefore, in order to assure the In content of not less than 5.2 mass%, which satisfies the in-vehicle requirement also in a combination withthe Au electrode, the Cu content is desirably not less than 0.50 mass %.When the Cu content is not less than 0.50 mass %, also in thecombination with the Au electrode, the In content after soldering is notless than 5.2 mass %, and the reliability of the in-vehicle requirementcan be satisfied.

As mentioned above, a case using the solder material having acomposition of Sn-3.5 mass % Ag-0.5 mass % Bi-6.0 mass % In isdescribed. The change amount of the In content when the Cu content is0.50 mass % is 0.8 mass %. Therefore, for example, when the soldermaterial having a composition of Sn-3.5 mass % Ag-0.5 mass % Bi-5.5 mass% In having different In contents is used, the In content aftersoldering is 4.7 mass %, and the reliability of the in-vehiclerequirement cannot be satisfied. In this way, as shown in FIG. 5, whenthe Cu content is not less than 0.5 mass % and not more than 1.0 mass %,the Cu content and the In content have correlation represented by theapproximate straight line therebetween. When the Cu content is less than0.5 mass % and more than 1.0 mass %, the correlation is not observed.

FIG. 7 is a graph showing a relation between the Cu content and the Incontent in the solder material in accordance with the embodiment.Hereinafter, the contents (mass %) of Ag, Bi, Cu, and In in the soldermaterial may be represented by [Ag], [Bi], [Cu], and [In], respectively.

The lower limit of the In content is determined for each range of threedivided ranges of the Cu content.

That is to say, when [Cu] falls within a range of 0<[Cu]<0.5, 6.0≦[In]is satisfied.

Furthermore, when [Cu] falls within a range of 0.5≦[Cu]≦1.0,5.2+(6−(1.55×[Cu]+4.428))≦[In] is satisfied.

Furthermore, when [Cu] falls within a range of 1.0<[Cu], 5.2 [In] issatisfied.

On the other hand, the upper limit value of the In content also isdetermined for each range of three divided ranges of the Cu content.

That is to say, when [Cu] falls within the range of 0<[Cu]<0.5, [In]≦7.6is satisfied.

Furthermore, when [Cu] falls within the range of 0.5≦[Cu]≦1.0,[In]≦6.8+(6−(1.55×[Cu]+4.428)) is satisfied.

Furthermore, when [Cu] falls within the range of 1.0<[Cu], [In] ≦6.8 issatisfied.

As mentioned above, the combination including the Au electrode isdescribed. However, in the case of the Cu electrode, since a compound tobe reacted with In is not included, the In content is not reduced.

FIG. 8A is a sectional view schematically showing a structure before Cusubstrate electrode 220 of electronic circuit board 200 and Cu componentelectrode 320 of the electronic component are soldered to each other.Solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposedbetween Cu substrate electrode 220 and Cu component electrode 320. FIG.8B is a sectional view schematically showing a structure after Cusubstrate electrode 220 of electronic circuit board 200 and Cu componentelectrode 320 of the electronic component are soldered to each other.Cu₆Sn₅ compound 120 is generated between Cu substrate electrode 220 andsolder portion 110. The similar compound 120 is generated also betweenCu component electrode 320 and solder portion 110. Since In is notinvolved in the generation of Cu₆Sn₅ compound 120, the reduction in theIn content in solder material 100 does not occur. Note here that inFIGS. 8A and 8B, the electronic components are not shown.

As mentioned above, when the solder material of the present disclosureis used in a combination which does not include the Au electrode, the Incontent is not reduced, so that when the Cu content is not more than 1.0mass %, the In content may exceed 6.8 mass % as the in-vehiclerequirement. Therefore, in order to allow the solder material of thepresent disclosure to be used in both the combination including the Auelectrode and the combination that does not include the Au electrode, itis necessary to limit the In content to not more than 6.8 mass % whenthe Cu content is in the range of not more than 1.0 mass %.

Next, the upper limit of the Cu content is described with reference toFIG. 6.

When the Cu content is too large, since a temperature of liquid phaseline 602 is increased, the melting property of the solder material isreduced and the wet-spreading property is easily deteriorated.

Specifically, the liquid phase line temperature represented by liquidphase line 602 is increased when the Cu content exceeds 0.7 mass %, andthe temperature is 216° C. when the Cu content is 1.2 mass %, and 228°C. when the Cu content is 1.4 mass %. The solid phase line temperaturerepresented by solid phase line 601 is stable in a range from 199° C. to201° C.

Herein, the solid phase line temperature is a temperature at which aheated solder alloy starts to be melted from a solid state, and theliquid phase line temperature is a temperature at which all the heatedsolder alloy is completed to be melted from the solid state.

Table 1 shows relation between the Cu content and wet spread in thesolder material having a composition of Sn-3.5 mass % Ag-0.5 mass %Bi-6.0 mass % In to which Cu is added. Specifically, the wet spread onthe Au electrode is evaluated when the Cu content is 0.2 mass %, 0.5mass %, 0.7 mass %, 1.0 mass %, 1.2 mass %, 1.4 mass %, and 1.7 mass %,respectively.

As mentioned above, the mass of P contained in the Ni plating fluctuatesin proportion to the film thickness T of the Ni plating. Herein, thefilm thickness of the Ni plating approaches the lower limit, and thecontent of P becomes minimum. From this viewpoint, it is assumed thatthe wet-spreading property is not excellent. Therefore, in the testsamples produced so that the film thickness of the Ni plating is 1 μm, awet-spreading rate is measured by a spread testing method specified in“Solder flux test method” of JIS Z 3197.

TABLE 1 Cu content (mass %) 0.2 0.5 0.7 1.0 1.2 1.4 1.7 Wet spread W3 W3W3 W3 W3 W2 W1

In Table 1, in evaluation of the wet spread, “W3” shows that thewet-spread rate is not less than 90%, “W2” shows that the wet-spreadrate is not less than 85% and less than 90%, and “W1” shows that thewet-spread rate is less than 85%, respectively.

From Table 1, in order to assure the wet-spread rate of not less than90%, which is important for excellent soldering, the Cu content isdesirably not more than 1.2 mass %.

FIG. 9 is a graph showing relation between the Cu content and the Incontent in the solder material in accordance with the embodiment inwhich 1.2 mass % as the upper limit value of the Cu content is added toFIG. 7. That is to say, in FIG. 9, a hatched area satisfies the Cucontent and the In content of the solder material of the presentdisclosure. The hatched area includes solid lines but does not includebroken lines and white points (o).

Table 2 shows the relation between the compositions of various types ofsolder material before soldering and the change of the In content aftersoldering, as well as the results of the reliability determination andthe strength determination in a combination of the Au substrateelectrode and the Au component electrode. Samples include 17 samples ofExamples 1 to 13 and Comparative Examples 1 to 4.

As to the strength determination, based on the tensile strength of thesolder material, “S1” shows that the tensile strength satisfies not lessthan 60 MPa enabling use in chip components having a size of up to 0.9mm×0.8 mm. “S2” shows that the tensile strength satisfies not less than65 MPa enabling use in large-size semiconductor components such as QFP(Quad Flat Package) and BGA (Ball Grid Array). “S3” shows that thetensile strength satisfies not less than 70 MPa enabling use inlarge-size components such as aluminum electrolytic capacitors andmodule components. “S4” shows that the tensile strength satisfies notless than 75 MPa enabling use in large-size components such as coils andtransformers. Note here that the tensile strength is measured by using aNo. 4 test piece of JIS Z 2201.

TABLE 2 Content and reduction Contents of component elements rate of Inafter in solder material before soldering (mass %) Reliabilitydetermination Strength determination soldering (mass %) Reduction Number2000 cyc 2250 cyc Tensile strength Sn Ag In Bi Cu In Det. rate of In ofcycles or more or more (MPa) Det. Ex. 1 Bal. 3.5 5.9 0.5 0.80 5.5 G −0.42200 G NG 70.4 S3 Ex. 2 Bal. 2.6 6.8 0.3 0.50 6.0 G −0.8 2300 G G 66.3S2 Ex. 3 Bal. 0.5 6.7 0.3 0.20 5.9 G −0.8 2250 G G 61.4 S1 Ex. 4 Bal.2.2 6.8 0.7 1.20 6.8 G 0.0 2000 G NG 76.5 S4 Ex. 5 Bal. 3.8 6.0 0.6 1.105.9 G −0.1 2250 G G 77.1 S4 Ex. 6 Bal. 3.0 6.5 0.2 0.95 6.3 G −0.2 2250G G 74.9 S3 Ex. 7 Bal. 0.7 6.6 0.9 0.60 5.9 G −0.7 2250 G G 66.3 S2 Ex.8 Bal. 1.8 6.7 0.7 0.80 6.3 G −0.4 2250 G G 71.3 S3 Ex. 9 Bal. 1.0 5.31.0 1.00 5.3 G 0.0 2000 G NG 75.1 S4 Ex. 10 Bal. 1.8 6.0 0.4 0.50 5.2 G−0.8 2000 G NG 68.3 S2 Ex. 11 Bal. 3.5 6.1 1.0 1.20 6.0 G −0.1 2300 G G78.6 S4 Ex. 12 Bal. 3.0 5.2 0.8 1.20 5.2 G 0.0 2000 G NG 76.7 S4 Ex. 13Bal. 0.7 6.3 0.8 0.40 5.5 G −0.8 2100 G NG 63.4 S1 CEx. 1 Bal. 3.5 5.70.5 0.20 4.9 NG −0.8 1650 NG NG 74.8 S3 CEx. 2 Bal. 2.8 5.5 0.3 0.50 4.7NG −0.8 1500 NG NG 64.1 S1 CEx. 3 Bal. 3.0 5.8 0.8 0.40 5.0 NG −0.8 1850NG NG 74.9 S3 CEx. 4 Bal. 3.5 5.9 0.5 — 5.1 NG −0.8 1950 NG NG 60.7 S1Ex. = Example, CEx. = Comparative Example, Bal = balance, cyc = cycles,Det. = determination

A balance after the In content is changed is measured by analyzing theIn content inside the solder portion by using EDX after soldering to theAu electrode is carried out.

In the determination of the change of the In content, “G (Good)” showsthat the In content after soldering falls in a range of 5.2 to 6.8 mass%, and “NG (No Good)” shows that the In content falls in a range of lessthan 5.2 mass %.

As to the reliability determination, the reliability test ofvehicle-mounted products is based on the requirements specification thatthe number of cycles of the heat cycle test satisfies not less than 2000cycles or not less than 2250 cycles. “G (Good)” shows that therequirement is satisfied and “NG (No Good)” shows that the requirementis not satisfied.

Results of the reliability determination of Examples 1 to 13 show thatwhen the solder material having a composition of Sn—Ag—Bi—In contains apredetermined amount of Cu, reduction of the In content is suppressed.Therefore, it is demonstrated that any of Examples 1 to 13 satisfy notless than 2000 cycles of the requirements specification.

In Comparative Examples 1 to 4, since addition of an element necessaryfor suppressing reduction of the In content is not carried out, the Incontent after soldering is 4.7 to 5.1 mass % (change of the In contentis −0.8 mass %). That is to say, it is demonstrated that not less than2000 cycles of the requirements specification is not satisfied.

Next, Table 3 shows the relation between the compositions of varioustypes of solder material before soldering and the change of the Incontent after soldering, as well as the results of the reliabilitydetermination and the strength determination in a combination of the Ausubstrate electrode and the Cu component electrode. Samples include 17samples of Examples 14 to 26 and Comparative Examples 5 to 8. Eachdetermination is the same as that of Table 2 mentioned above.

TABLE 3 Content and reduction Contents of component elements rate of Inafter in solder material before soldering (mass %) Reliabilitydetermination Strength determination soldering (mass %) Reduction Number2000 cyc 2250 cyc Tensile strength Sn Ag In Bi Cu In Det. rate of In ofcycles or more or more (MPa) Det. Ex. 14 Bal. 3.5 5.9 0.5 0.80 5.5 G−0.3 2200 G NG 70.6 S3 Ex. 15 Bal. 2.6 6.8 0.3 0.50 6.0 G −0.8 2300 G G66.2 S2 Ex. 16 Bal. 0.5 6.7 0.3 0.20 5.9 G −0.8 2250 G G 61.2 S1 Ex. 17Bal. 2.2 6.8 0.7 1.20 6.8 G 0.0 2000 G NG 76.7 S4 Ex. 18 Bal. 3.8 6.00.6 1.10 5.9 G −0.1 2250 G G 77.3 S4 Ex. 19 Bal. 3.0 6.5 0.2 0.95 6.3 G−0.2 2250 G G 74.9 S3 Ex. 20 Bal. 0.7 6.6 0.9 0.60 6.0 G −0.6 2250 G G66.2 S2 Ex. 21 Bal. 1.8 6.7 0.7 0.80 6.3 G −0.4 2250 G G 71.5 S3 Ex. 22Bal. 1.0 5.3 1.0 1.00 5.3 G 0.0 2000 G NG 75.2 S4 Ex. 23 Bal. 1.8 6.00.4 0.50 5.2 G −0.8 2000 G NG 68.5 S1 Ex. 24 Bal. 3.5 6.1 1.0 1.20 6.0 G−0.1 2300 G G 78.8 S4 Ex. 25 Bal. 3.0 5.2 0.8 1.20 5.2 G 0.0 2000 G NG76.7 S4 Ex. 26 Bal. 0.7 6.3 0.8 0.40 5.5 G −0.8 2100 G NG 63.6 S1 CEx. 5Bal. 3.5 5.7 0.5 0.20 4.9 NG −0.8 1650 NG NG 74.9 S3 CEx. 6 Bal. 2.8 5.50.3 0.30 4.7 NG −0.8 1500 NG NG 64.3 S1 CEx. 7 Bal. 3.0 5.8 0.8 0.40 5.0NG −0.8 1850 NG NG 74.9 S3 CEx. 8 Bal. 3.5 5.9 0.5 — 5.1 NG −0.8 1950 NGNG 60.8 S1 Ex. = Example, CEx. = Comparative Example, Bal = balance, cyc= cycles, Det. = determination

Results of the reliability determination of Examples 14 to 26 show thatwhen the solder material having a composition of Sn—Ag—Bi—I contains apredetermined amount of Cu, reduction of the In content is suppressed.Therefore, it is demonstrated that any of Examples 14 to 26 satisfy notless than 2000 cycles of the requirements specification. Examples 14 to26 show a combination of the Au substrate electrode and the Cu componentelectrode, but it is thought that the same results are obtained in acombination of the Cu substrate electrode and the Au componentelectrode.

In Comparative Examples 5 to 8, since addition of an element necessaryfor suppressing reduction of the In content is not carried out, the Incontent after soldering is 4.7 to 5.1 mass % (change of the In contentis −0.8 mass %). That is to say, it is demonstrated that not less than2000 cycles of the requirements specification is not satisfied.

Next, Table 4 shows the relation between the compositions of varioustypes of solder material that does not contain Bi and the change of theIn content, as well as the results of the reliability determination andthe strength determination in a combination of the Au substrateelectrode and Au component electrode. Samples include 13 samples ofExamples 27 to 39.

TABLE 4 Content and reduction Contents of component elements rate of Inafter in solder material before soldering (mass %) Reliabilitydetermination Strength determination soldering (mass %) Reduction Number2000 cyc 2250 cyc Tensile strength Sn Ag In Bi Cu In Det. rate of In ofcycles or more or more (MPa) Det. Ex. 27 Bal. 0.7 5.9 — 0.75 5.5 G −0.52150 G NG 65.6 S2 Ex. 28 Bal. 4.0 5.6 — 1.00 5.5 G −0.1 2200 G NG 74.3S3 Ex. 29 Bal. 0.3 6.0 — 0.50 5.2 G −0.8 2000 G NG 66.3 S2 Ex. 30 Bal.2.9 6.0 — 0.90 5.8 G −0.2 2250 G G 72.4 S3 Ex. 31 Bal. 3.5 5.6 — 1.205.6 G 0.0 2200 G NG 76.2 S4 Ex. 32 Bal. 0.5 6.8 — 0.60 6.2 G −0.6 2250 GG 67.5 S2 Ex. 33 Bal. 1.2 5.8 — 1.20 5.4 G −0.1 2100 G NG 77.1 S4 Ex. 34Bal. 3.2 6.2 — 1.10 6.1 G −0.1 2300 G G 75.7 S4 Ex. 35 Bal. 1.1 6.1 —0.40 5.3 G −0.8 2100 G NG 61.8 S1 Ex. 36 Bal. 2.1 6.5 — 0.95 6.4 G −0.12200 G NG 73.3 S3 Ex. 37 Bal. 1.9 6.6 — 0.70 6.0 G −0.6 2300 G G 67.3 S2Ex. 38 Bal. 2.8 6.1 — 0.85 5.9 G −0.2 2250 G G 73.9 S3 Ex. 39 Bal. 0.56.2 — 0.30 5.4 G −0.8 2100 G NG 63.7 S1 Ex. = Example, CEx. =Comparative Example, Bal = balance, cyc = cycles, Det. = determination

In Examples 27 to 39 of Table 4, since all the results of thereliability determination satisfy the requirement of not less than 2000cycles, it is shown that the change in the In content is not influencedeven if Bi is not contained in the solder material. Bi is added toadjust the melting temperature of the solder material, the content of Bidoes not have a large influence on the thermal fatigue properties of thesolder material.

From the results of the reliability determination shown in Examples 1 to39 of Tables 2 to 4, in order to satisfy the reliability evaluation ofvehicle-mounted products in soldering to the Au electrode and the Cuelectrode, the solder material having a composition of Sn—Ag—Bi—Inbefore soldering satisfies the following relation.

That is to say, the solder material includes:

Ag satisfying 0.3≦[Ag]≦4.0;

Bi satisfying 0≦[Bi]≦1.0; and

Cu satisfying 0<[Cu]≦1.2.

When the solder material includes In in the range of 6.0≦[In] 6.8 when[Cu] falls within a range of 0<[Cu]<0.5;

in the range of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu] fallswithin a range of 0.5≦[Cu]≦1.0;

in the range of 5.2≦[In]≦6.8 when [Cu] falls within a range of1.0<[Cu]≦1.2; and

a balance includes only not less than 87 mass % of Sn, the requirementof the reliability determination after soldering (not less than 2000cycles) can be satisfied.

Furthermore, the content of Ag constituting the solder material inaccordance with this embodiment is determined by the following reasons.

As already described, since the thermal fatigue properties are improvedby the solid solution effect of In on Sn, the thermal fatigue propertiesare largely changed by the In content. However, since Ag is notsolid-dissolved in Sn, the thermal fatigue properties are not largelychanged.

Furthermore, since the Ag content has an influence on the melting pointof the solder material, the melting point is 235° C. or higher when theAg content exceeds 4 mass %. Thus, wet spread at the time of solderingis deteriorated, so that the soldering material cannot be used.Therefore, a maximum value of the Ag content is made to be 4 mass %.Furthermore, when the Ag content becomes smaller, a deposited amount ofAg₃Sn to a Sn phase is reduced, and the property of the mechanicalstrength is lowered. Therefore, the minimum value of the Ag content ismade to be 0.3 mass %.

Next, the content of Bi constituting the solder material in accordancewith this embodiment is determined by the following reason. As describedin Table 4, the minimum value can be zero from the viewpoint thatthermal fatigue properties of the solder material are not influenced.Furthermore, since Bi has a property of segregating inside the solderalloy, when Bi is more than 1 mass %, a segregating amount is increasedand an alloy become brittle and cannot be used. Consequently, themaximum value of the Bi content is made to be 1 mass %.

As mentioned above, Ag and Bi do not have a large influence on thethermal fatigue properties of the solder material. Therefore, it isthought that an effect of the In content in the solder material having acomposition of Sn—Ag—Bi—In can be handled similarly in the soldermaterial having a composition of Sn—Ag—In or a composition of Sn—Bi—In.However, since the Ag content is zero in the solder material having thecomposition of Sn—Bi—In, the mechanical strength may be deteriorated.

As is apparent from the above description, the solder material of thepresent disclosure can be suitably used in soldering of the Au electrodeincluding Ni plating containing P. The Au electrode in this case may beany of the Au substrate electrode and the Au component electrode.Furthermore, the Ni plating includes 3 to 15 mass % P, preferably 5 to10 mass % P, and balance has a composition of Ni.

Furthermore, the above-mentioned solder material includes:

Ag satisfying 0.3≦[Ag]≦4.0;

Bi satisfying 0≦[Bi]≦1.0; and

Cu satisfying 0<[Cu]≦1.2.

Moreover, the solder material includes In in the range of 6.0≦[In]≦6.8when [Cu] falls within a range of 0<[Cu]<0.5;

in the range of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu] fallswithin a range of 0.5≦[Cu]≦1.0;

in the range of 5.2≦[In]≦6.8 when [Cu] falls within a range of1.0<[Cu]≦1.2, and a balance includes only not less than 87 mass % of Sn.

When the above-mentioned solder material is used in soldering of the Cuelectrode, the In content is not reduced. Therefore, the above-mentionedsolder material can be suitably used also for a combination of the Cusubstrate electrode and the Cu component electrode. Thus, according tothe solder material of the present disclosure, even if the Au electrodeand the Cu electrode are mixed when the electronic circuit board and theelectronic component are bonded to each other by soldering, a solderportion having excellent thermal fatigue properties can be formed.

A slight amount of Cu may be contained for preventing Cu in theelectrode from being eroded, but the lower limit value of the Cu contentis preferably not less than 0.5 mass % at which the tensile strengthsatisfies not less than 65 MPa and large-size semiconductor componentssuch as QFP and BGA can be used.

In particular, it is preferable that the solder material includes:

-   -   0.5 to 3.8 mass % of Ag;    -   0.2 to 1.0 mass % of Bi;    -   6.0 to 6.8 mass % of In; and    -   0.2 to 1.2 mass % of Cu, wherein the balance includes only not        less than 87.2 mass % of Sn.

Specific examples of the solder material include material of Examples 2,3, 5 to 8, 11 in Table 2. The solder material satisfies a more stringentrequirement of the reliability determination (not less than 2250cycles).

Furthermore, it is more preferable that the solder material includes:

-   -   1.8 to 3.8 mass % of Ag;    -   0.2 to 1.0 mass % of Bi;    -   6.0 to 6.7 mass % of In; and    -   0.8 to 1.2 mass % of Cu, wherein the balance includes only not        less than 87.3 mass % of Sn.

Specific examples of the solder material include material of Examples 5,6, 8, and 11 in Table 2. The solder material satisfies a more stringentrequirement of the reliability determination (not less than 2250cycles), and the tensile strength satisfies not less than 70 MPaenabling the use in large-size components such as aluminum electrolyticcapacitors and module components.

Furthermore, it is further preferable that the solder material includes:

-   -   3.5 to 3.8 mass % of Ag;    -   0.6 to 1.0 mass % of Bi;    -   6.0 to 6.1 mass % of In; and    -   1.1 to 1.2 mass % of Cu, wherein the balance includes only not        less than 87.9 mass % of Sn.

Specific examples of the solder material include material of Examples 5and 11 in Table 2. The solder material satisfies a more stringentrequirement of the reliability determination (not less than 2250cycles), and the tensile strength also satisfies not less than 75 MPaenabling the use in large-size components such as coils andtransformers.

Furthermore, it is preferable that when Bi is not included, the soldermaterial includes:

-   -   0.5 to 3.2 mass % of Ag;    -   6.0 to 6.8 mass % of In; and    -   0.6 to 1.1 mass % of Cu, wherein the balance includes only not        less than 88.9 mass % of Sn.

Specific examples of the solder material include material of Examples30, 32, 34, 37, and 38 in Table 4. The solder material satisfies a morestringent requirement of the reliability determination (not less than2250 cycles).

Furthermore, it is more preferable that when Bi is not included, thesolder material includes:

-   -   2.8 to 3.2 mass % of Ag;    -   6.0 to 6.2 mass % of In; and    -   0.85 to 1.1 mass % of Cu, wherein the balance includes only not        less than 89.5 mass % of Sn.

Specific examples of the solder material include material of Examples30, 34, and 38 in Table 4. The solder material satisfies a morestringent requirement of the reliability determination (not less than2250 cycles), and the tensile strength also satisfies not less than 70MPa enabling the use in large-size components such as aluminumelectrolytic capacitors and module components.

A bonded structure of the present disclosure includes an electroniccircuit board having a substrate electrode, and an electronic componenthaving a component electrode. Herein, examples of the electronic circuitboard include patterned insulating substrates of various FR grades.Furthermore, examples of the electronic component include large-sizesemiconductor components such as chip components, QFP, and BGA,large-size components such as aluminum electrolytic capacitors andmodule components, large-size components such as coils and transformers,and the like.

In the above-mentioned bonded structure, at least one of the substrateelectrode and the component electrode is an Au electrode. For example, acase where the substrate electrode is an Au electrode (Au substrateelectrode) and the component electrode is a Cu electrode (Cu componentelectrode), a case where the substrate electrode is a Cu electrode (Cusubstrate electrode) and the component electrode is an Au electrode (Aucomponent electrode), and a case where the substrate electrode is an Auelectrode (Au substrate electrode) and the component electrode is an Auelectrode (Au component electrode) are included.

In the above-mentioned bonded structure, the substrate electrode and thecomponent electrode are bonded to each other with the solder material ofthe present disclosure. The solder material of the present disclosuresatisfies reliability evaluation of vehicle-mounted products insoldering to the Au electrode and Cu electrode from the results of thereliability determination shown in Tables 2 to 4 and Examples 1 to 39 asmentioned above. Therefore, when the electronic circuit board and theelectronic component are bonded to each other by soldering, even if boththe Au electrode and the Cu electrode are mixed, a solder portion havingexcellent thermal fatigue properties can be formed. Note here that thecontent of Cu contained in the solder material can be appropriatelychanged according to the content of P contained in the Ni plating of theAu electrode.

FIG. 10 is a sectional view schematically showing bonded structure 700in accordance with the embodiment.

Bonded structure 700 is configured by bonding electronic circuit board730 provided with Au substrate electrodes 731 and 732 and electroniccomponent 720 having Cu component electrodes 721 and electroniccomponent 740 having Au component electrodes 741 to each other bysoldering. In bonded structure 700, Au substrate electrodes 731 ofelectronic circuit board 730 and Cu component electrodes 721 ofelectronic component 720 are bonded to each other with solder portions711. Furthermore, Au substrate electrodes 732 of electronic circuitboard 730 and Au component electrodes 741 of electronic component 740are bonded to each other with solder portions 712. Solder portions 711and 712 are formed of the solder material having a composition ofSn—Ag—Bi—In—Cu or Sn—Ag—In—Cu in accordance with the present disclosure.As is apparent from the results of the reliability determination shownin Examples 1 to 39 of Tables 2 to 4, bonded structure 700 satisfies therequirements specification of the reliability test of a vehicle-mountedproduct. In bonded structure 700, Au substrate electrodes 731 and 732may be a Cu substrate electrode.

FIG. 11A is a sectional view schematically showing a structure before Ausubstrate electrode 210 of electronic circuit board 200 and Cu componentelectrode 320 of the electronic component are soldered to each other. Ausubstrate electrode 210 is provided with Cu electrode 211, Ni plating212, and Au flash plating 213 from an electronic circuit board 200 side.Solder material 100 having a composition of Sn—Ag—Bi—In—Cu is interposedbetween Au substrate electrode 210 and Cu component electrode 320.

FIG. 11B is a sectional view schematically showing a structure after Ausubstrate electrode 210 of electronic circuit board 200 and Cu componentelectrode 320 of the electronic component are soldered to each other. Ausubstrate electrode 210 includes Ni plating 212 containing P. Aftersoldering, (Cu,Ni)Sn compound 130 such as (Cu_(0.7),Ni_(0.3))₆Sn₅ isgenerated between Au substrate electrode 210 and the solder portion.This (Cu,Ni)Sn compound 130 is useful for preventing the In content insolder material 100 from being reduced. On the other hand, Cu₆Sn₅compound 120 is generated between Cu component electrode 320 and solderportion 110. Since In is not involved in the generation of Cu₆Sn₅compound 120, the In content of solder material 100 is not reduced. InFIGS. 11A and 11B, an electronic component is not shown.

FIG. 12A is a sectional view schematically showing a structure before Cusubstrate electrode 220 of electronic circuit board 200 and Au componentelectrode 310 of the electronic component are soldered to each other. Aucomponent electrode 310 is provided with Cu electrode 311, Ni plating312, and Au flash plating 313 from an electronic component side. Soldermaterial 100 having a composition of Sn—Ag—Bi—In—Cu is interposedbetween Cu substrate electrode 220 and Au component electrode 310.

FIG. 12B is a sectional view schematically showing a structure after Cusubstrate electrode 220 of electronic circuit board 200 and Au componentelectrode 310 of the electronic component are soldered to each other. Aucomponent electrode 310 includes Ni plating 312 containing P. Aftersoldering, (Cu,Ni)Sn compound 130 such as (Cu_(0.7),Ni_(0.3))₆Sn₅ isgenerated between Au component electrode 310 and solder portion 110.This (Cu,Ni)Sn compound 130 is useful for preventing the In content insolder material 100 from being reduced. On the other hand, Cu₆Sn₅compound 120 is generated between Cu substrate electrode 220 and solderportion 110. Since In is not involved in the generation of Cu₆Sn₅compound 120, the In content of solder material 100 is not reduced. InFIGS. 12A and 12B, an electronic component is not shown.

FIG. 13A is a sectional view schematically showing a structure before Ausubstrate electrode 210 of electronic circuit board 200 and Au componentelectrode 310 of the electronic component are soldered to each other. Ausubstrate electrode 210 is provided with Cu electrode 211, Ni plating212, and Au flash plating 213 from an electronic circuit board 200 side.Au component electrode 310 is provided with Cu electrode 311, Ni plating312, and Au flash plating 313 from an electronic component side. Soldermaterial 100 having a composition of Sn—Ag—Bi—In—Cu is interposedbetween Au substrate electrode 210 and Au component electrode 310.

FIG. 13B is a sectional view schematically showing a structure after Ausubstrate electrode 210 of electronic circuit board 200 and Au componentelectrode 310 of the electronic component are soldered to each other. Ausubstrate electrode 210 includes Ni plating 212 containing P. Aftersoldering, (Cu,Ni)Sn compound 130 such as (Cu_(0.7), Ni_(0.3))₆Sn₅ isgenerated between Au substrate electrode 210 and solder portion 110after soldering. Similarly, Au component electrode 310 includes Niplating 312 containing P, but (Cu,Ni)Sn compound 130 such as(Cu_(0.7),Ni_(0.3))₆Sn₅ is generated between Au component electrode 310and solder portion 110 after soldering. This (Cu,Ni)Sn compound 130 isuseful for preventing the In content in solder material 100 from beingreduced. In FIGS. 13A and 13B, an electronic component is not shown.

Solder material and a bonded structure in accordance with the presentdisclosure can form a solder portion having excellent thermal fatigueproperties even if an Au electrode and a Cu electrode are mixed when anelectronic circuit board and an electronic component are bonded to eachother by soldering. For example, they are suitably used in paste or thelike to be used in soldering.

What is claimed is:
 1. Solder material comprising: Ag (silver)satisfying 0.3≦[Ag]<4.0; where 0.5 mass % and 1.0 mass % of Ag areexcluded, Bi (bismuth) satisfying 0≦[Bi]≦1.0; and Cu (copper) satisfying0.2≦[Cu]≦1.2; and further comprising: In (indium) in a range of6.0≦[In]≦6.8 when [Cu] falls within a range of 0.2≦[Cu]<0.5; In in arange of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu] falls within arange of 0.5≦[Cu]≦1.0; In in a range of 5.2≦[In]≦6.8 when [Cu] fallswithin a range of 1.0<[Cu]≦1.2, with a balance including 87≦[Sn], wherecontents (mass %) of Ag, Bi, Cu, In, and Sn (tin) in the solder materialare denoted by [Ag], [Bi], [Cu], [In] and [Sn], respectively.
 2. Thesolder material of claim 1, wherein Ag satisfies 0.5≦[Ag]≦3.8, Bisatisfies 0.2≦[Bi]≦1.0, In satisfies 6.0≦[In]≦6.8, Cu satisfies0.2≦[Cu]≦1.2, and a balance includes only not less than 87.2 mass % ofSn.
 3. The solder material of claim 1, wherein Ag satisfies1.8≦[Ag]≦3.8, Bi satisfies 0.2≦[Bi]≦1.0, In satisfies 6.0≦[In]≦6.7, Cusatisfies 0.8≦[Cu]≦1.2, and a balance includes only not less than 87.3mass % of Sn.
 4. The solder material of claim 1, wherein Ag satisfies3.5≦[Ag]≦3.8, Bi satisfies 0.6≦[Bi]≦1.0, In satisfies 6.0≦[In]≦6.1, Cusatisfies 1.1≦[Cu]≦1.2, and a balance includes only not less than 87.9mass % of Sn.
 5. The solder material of claim 1, wherein Bi satisfies[Bi]=0, Ag satisfies 0.5≦[Ag]≦3.2, In satisfies 6.0≦[In]≦6.8, Cusatisfies 0.6≦[Cu]≦1.1, and a balance includes only not less than 88.9mass % of Sn.
 6. The solder material of claim 1, wherein Bi satisfies[Bi]=0, Ag satisfies 2.8≦[Ag]≦3.2, In satisfies 6.0≦[In]≦6.2, Cusatisfies 0.85≦[Cu]≦1.1, and a balance includes only not less than 89.5mass % of Sn.
 7. A bonded structure comprising: solder material definedin claim 1; an electronic circuit board having a plurality of substrateelectrodes; and an electronic component having a plurality of componentelectrodes, wherein any of the plurality of substrate electrodes and theplurality of component electrodes is the Au electrode including Niplating containing P (phosphorous), and the plurality of substrateelectrodes and the plurality of component electrodes are bonded to eachother with the solder material.
 8. A bonded structure comprising: soldermaterial defined in claim 2; an electronic circuit board having aplurality of substrate electrodes; and an electronic component having aplurality of component electrodes, wherein any of the plurality ofsubstrate electrodes and the plurality of component electrodes is the Auelectrode including Ni plating containing P (phosphorous), and theplurality of substrate electrodes and the plurality of componentelectrodes are bonded to each other with the solder material.
 9. Abonded structure comprising: solder material defined in claim 3; anelectronic circuit board having a plurality of substrate electrodes; andan electronic component having a plurality of component electrodes,wherein any of the plurality of substrate electrodes and the pluralityof component electrodes is the Au electrode including Ni platingcontaining P (phosphorous), and the plurality of substrate electrodesand the plurality of component electrodes are bonded to each other withthe solder material.
 10. A bonded structure comprising: solder materialdefined in claim 4; an electronic circuit board having a plurality ofsubstrate electrodes; and an electronic component having a plurality ofcomponent electrodes, wherein any of the plurality of substrateelectrodes and the plurality of component electrodes is the Au electrodeincluding Ni plating containing P (phosphorous), and the plurality ofsubstrate electrodes and the plurality of component electrodes arebonded to each other with the solder material.
 11. A bonded structurecomprising: solder material defined in claim 5; an electronic circuitboard having a plurality of substrate electrodes; and an electroniccomponent having a plurality of component electrodes, wherein any of theplurality of substrate electrodes and the plurality of componentelectrodes is the Au electrode including Ni plating containing P(phosphorous), and the plurality of substrate electrodes and theplurality of component electrodes are bonded to each other with thesolder material.
 12. A bonded structure comprising: solder materialdefined in claim 6; an electronic circuit board having a plurality ofsubstrate electrodes; and an electronic component having a plurality ofcomponent electrodes, wherein any of the plurality of substrateelectrodes and the plurality of component electrodes is the Au electrodeincluding Ni plating containing P (phosphorous), and the plurality ofsubstrate electrodes and the plurality of component electrodes arebonded to each other with the solder material.